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1// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
2/*
3 * Ring buffer operations.
4 *
5 * Copyright (C) 2020 Facebook, Inc.
6 */
7#ifndef _GNU_SOURCE
8#define _GNU_SOURCE
9#endif
10#include <stdlib.h>
11#include <stdio.h>
12#include <errno.h>
13#include <unistd.h>
14#include <linux/err.h>
15#include <linux/bpf.h>
16#include <asm/barrier.h>
17#include <sys/mman.h>
18#include <sys/epoll.h>
19#include <time.h>
20
21#include "libbpf.h"
22#include "libbpf_internal.h"
23#include "bpf.h"
24
25struct ring {
26 ring_buffer_sample_fn sample_cb;
27 void *ctx;
28 void *data;
29 unsigned long *consumer_pos;
30 unsigned long *producer_pos;
31 unsigned long mask;
32 int map_fd;
33};
34
35struct ring_buffer {
36 struct epoll_event *events;
37 struct ring **rings;
38 size_t page_size;
39 int epoll_fd;
40 int ring_cnt;
41};
42
43struct user_ring_buffer {
44 struct epoll_event event;
45 unsigned long *consumer_pos;
46 unsigned long *producer_pos;
47 void *data;
48 unsigned long mask;
49 size_t page_size;
50 int map_fd;
51 int epoll_fd;
52};
53
54/* 8-byte ring buffer header structure */
55struct ringbuf_hdr {
56 __u32 len;
57 __u32 pad;
58};
59
60static void ringbuf_free_ring(struct ring_buffer *rb, struct ring *r)
61{
62 if (r->consumer_pos) {
63 munmap(r->consumer_pos, rb->page_size);
64 r->consumer_pos = NULL;
65 }
66 if (r->producer_pos) {
67 munmap(r->producer_pos, rb->page_size + 2 * (r->mask + 1));
68 r->producer_pos = NULL;
69 }
70
71 free(r);
72}
73
74/* Add extra RINGBUF maps to this ring buffer manager */
75int ring_buffer__add(struct ring_buffer *rb, int map_fd,
76 ring_buffer_sample_fn sample_cb, void *ctx)
77{
78 struct bpf_map_info info;
79 __u32 len = sizeof(info);
80 struct epoll_event *e;
81 struct ring *r;
82 __u64 mmap_sz;
83 void *tmp;
84 int err;
85
86 memset(&info, 0, sizeof(info));
87
88 err = bpf_map_get_info_by_fd(map_fd, &info, &len);
89 if (err) {
90 err = -errno;
91 pr_warn("ringbuf: failed to get map info for fd=%d: %s\n",
92 map_fd, errstr(err));
93 return libbpf_err(err);
94 }
95
96 if (info.type != BPF_MAP_TYPE_RINGBUF) {
97 pr_warn("ringbuf: map fd=%d is not BPF_MAP_TYPE_RINGBUF\n",
98 map_fd);
99 return libbpf_err(-EINVAL);
100 }
101
102 tmp = libbpf_reallocarray(rb->rings, rb->ring_cnt + 1, sizeof(*rb->rings));
103 if (!tmp)
104 return libbpf_err(-ENOMEM);
105 rb->rings = tmp;
106
107 tmp = libbpf_reallocarray(rb->events, rb->ring_cnt + 1, sizeof(*rb->events));
108 if (!tmp)
109 return libbpf_err(-ENOMEM);
110 rb->events = tmp;
111
112 r = calloc(1, sizeof(*r));
113 if (!r)
114 return libbpf_err(-ENOMEM);
115 rb->rings[rb->ring_cnt] = r;
116
117 r->map_fd = map_fd;
118 r->sample_cb = sample_cb;
119 r->ctx = ctx;
120 r->mask = info.max_entries - 1;
121
122 /* Map writable consumer page */
123 tmp = mmap(NULL, rb->page_size, PROT_READ | PROT_WRITE, MAP_SHARED, map_fd, 0);
124 if (tmp == MAP_FAILED) {
125 err = -errno;
126 pr_warn("ringbuf: failed to mmap consumer page for map fd=%d: %s\n",
127 map_fd, errstr(err));
128 goto err_out;
129 }
130 r->consumer_pos = tmp;
131
132 /* Map read-only producer page and data pages. We map twice as big
133 * data size to allow simple reading of samples that wrap around the
134 * end of a ring buffer. See kernel implementation for details.
135 */
136 mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
137 if (mmap_sz != (__u64)(size_t)mmap_sz) {
138 err = -E2BIG;
139 pr_warn("ringbuf: ring buffer size (%u) is too big\n", info.max_entries);
140 goto err_out;
141 }
142 tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ, MAP_SHARED, map_fd, rb->page_size);
143 if (tmp == MAP_FAILED) {
144 err = -errno;
145 pr_warn("ringbuf: failed to mmap data pages for map fd=%d: %s\n",
146 map_fd, errstr(err));
147 goto err_out;
148 }
149 r->producer_pos = tmp;
150 r->data = tmp + rb->page_size;
151
152 e = &rb->events[rb->ring_cnt];
153 memset(e, 0, sizeof(*e));
154
155 e->events = EPOLLIN;
156 e->data.fd = rb->ring_cnt;
157 if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, e) < 0) {
158 err = -errno;
159 pr_warn("ringbuf: failed to epoll add map fd=%d: %s\n",
160 map_fd, errstr(err));
161 goto err_out;
162 }
163
164 rb->ring_cnt++;
165 return 0;
166
167err_out:
168 ringbuf_free_ring(rb, r);
169 return libbpf_err(err);
170}
171
172void ring_buffer__free(struct ring_buffer *rb)
173{
174 int i;
175
176 if (!rb)
177 return;
178
179 for (i = 0; i < rb->ring_cnt; ++i)
180 ringbuf_free_ring(rb, rb->rings[i]);
181 if (rb->epoll_fd >= 0)
182 close(rb->epoll_fd);
183
184 free(rb->events);
185 free(rb->rings);
186 free(rb);
187}
188
189struct ring_buffer *
190ring_buffer__new(int map_fd, ring_buffer_sample_fn sample_cb, void *ctx,
191 const struct ring_buffer_opts *opts)
192{
193 struct ring_buffer *rb;
194 int err;
195
196 if (!OPTS_VALID(opts, ring_buffer_opts))
197 return errno = EINVAL, NULL;
198
199 rb = calloc(1, sizeof(*rb));
200 if (!rb)
201 return errno = ENOMEM, NULL;
202
203 rb->page_size = getpagesize();
204
205 rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
206 if (rb->epoll_fd < 0) {
207 err = -errno;
208 pr_warn("ringbuf: failed to create epoll instance: %s\n", errstr(err));
209 goto err_out;
210 }
211
212 err = ring_buffer__add(rb, map_fd, sample_cb, ctx);
213 if (err)
214 goto err_out;
215
216 return rb;
217
218err_out:
219 ring_buffer__free(rb);
220 return errno = -err, NULL;
221}
222
223static inline int roundup_len(__u32 len)
224{
225 /* clear out top 2 bits (discard and busy, if set) */
226 len <<= 2;
227 len >>= 2;
228 /* add length prefix */
229 len += BPF_RINGBUF_HDR_SZ;
230 /* round up to 8 byte alignment */
231 return (len + 7) / 8 * 8;
232}
233
234static int64_t ringbuf_process_ring(struct ring *r, size_t n)
235{
236 int *len_ptr, len, err;
237 /* 64-bit to avoid overflow in case of extreme application behavior */
238 int64_t cnt = 0;
239 unsigned long cons_pos, prod_pos;
240 bool got_new_data;
241 void *sample;
242
243 cons_pos = smp_load_acquire(r->consumer_pos);
244 do {
245 got_new_data = false;
246 prod_pos = smp_load_acquire(r->producer_pos);
247 while (prod_pos - cons_pos > 0) {
248 len_ptr = r->data + (cons_pos & r->mask);
249 len = smp_load_acquire(len_ptr);
250
251 /* sample not committed yet, bail out for now */
252 if (len & BPF_RINGBUF_BUSY_BIT)
253 goto done;
254
255 got_new_data = true;
256 cons_pos += roundup_len(len);
257
258 if ((len & BPF_RINGBUF_DISCARD_BIT) == 0) {
259 sample = (void *)len_ptr + BPF_RINGBUF_HDR_SZ;
260 err = r->sample_cb(r->ctx, sample, len);
261 if (err < 0) {
262 /* update consumer pos and bail out */
263 smp_store_release(r->consumer_pos,
264 cons_pos);
265 return err;
266 }
267 cnt++;
268 }
269
270 smp_store_release(r->consumer_pos, cons_pos);
271
272 if (cnt >= n)
273 goto done;
274 }
275 } while (got_new_data);
276done:
277 return cnt;
278}
279
280/* Consume available ring buffer(s) data without event polling, up to n
281 * records.
282 *
283 * Returns number of records consumed across all registered ring buffers (or
284 * n, whichever is less), or negative number if any of the callbacks return
285 * error.
286 */
287int ring_buffer__consume_n(struct ring_buffer *rb, size_t n)
288{
289 int64_t err, res = 0;
290 int i;
291
292 for (i = 0; i < rb->ring_cnt; i++) {
293 struct ring *ring = rb->rings[i];
294
295 err = ringbuf_process_ring(ring, n);
296 if (err < 0)
297 return libbpf_err(err);
298 res += err;
299 n -= err;
300
301 if (n == 0)
302 break;
303 }
304 return res > INT_MAX ? INT_MAX : res;
305}
306
307/* Consume available ring buffer(s) data without event polling.
308 * Returns number of records consumed across all registered ring buffers (or
309 * INT_MAX, whichever is less), or negative number if any of the callbacks
310 * return error.
311 */
312int ring_buffer__consume(struct ring_buffer *rb)
313{
314 int64_t err, res = 0;
315 int i;
316
317 for (i = 0; i < rb->ring_cnt; i++) {
318 struct ring *ring = rb->rings[i];
319
320 err = ringbuf_process_ring(ring, INT_MAX);
321 if (err < 0)
322 return libbpf_err(err);
323 res += err;
324 if (res > INT_MAX) {
325 res = INT_MAX;
326 break;
327 }
328 }
329 return res;
330}
331
332/* Poll for available data and consume records, if any are available.
333 * Returns number of records consumed (or INT_MAX, whichever is less), or
334 * negative number, if any of the registered callbacks returned error.
335 */
336int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
337{
338 int i, cnt;
339 int64_t err, res = 0;
340
341 cnt = epoll_wait(rb->epoll_fd, rb->events, rb->ring_cnt, timeout_ms);
342 if (cnt < 0)
343 return libbpf_err(-errno);
344
345 for (i = 0; i < cnt; i++) {
346 __u32 ring_id = rb->events[i].data.fd;
347 struct ring *ring = rb->rings[ring_id];
348
349 err = ringbuf_process_ring(ring, INT_MAX);
350 if (err < 0)
351 return libbpf_err(err);
352 res += err;
353 }
354 if (res > INT_MAX)
355 res = INT_MAX;
356 return res;
357}
358
359/* Get an fd that can be used to sleep until data is available in the ring(s) */
360int ring_buffer__epoll_fd(const struct ring_buffer *rb)
361{
362 return rb->epoll_fd;
363}
364
365struct ring *ring_buffer__ring(struct ring_buffer *rb, unsigned int idx)
366{
367 if (idx >= rb->ring_cnt)
368 return errno = ERANGE, NULL;
369
370 return rb->rings[idx];
371}
372
373unsigned long ring__consumer_pos(const struct ring *r)
374{
375 /* Synchronizes with smp_store_release() in ringbuf_process_ring(). */
376 return smp_load_acquire(r->consumer_pos);
377}
378
379unsigned long ring__producer_pos(const struct ring *r)
380{
381 /* Synchronizes with smp_store_release() in __bpf_ringbuf_reserve() in
382 * the kernel.
383 */
384 return smp_load_acquire(r->producer_pos);
385}
386
387size_t ring__avail_data_size(const struct ring *r)
388{
389 unsigned long cons_pos, prod_pos;
390
391 cons_pos = ring__consumer_pos(r);
392 prod_pos = ring__producer_pos(r);
393 return prod_pos - cons_pos;
394}
395
396size_t ring__size(const struct ring *r)
397{
398 return r->mask + 1;
399}
400
401int ring__map_fd(const struct ring *r)
402{
403 return r->map_fd;
404}
405
406int ring__consume_n(struct ring *r, size_t n)
407{
408 int64_t res;
409
410 res = ringbuf_process_ring(r, n);
411 if (res < 0)
412 return libbpf_err(res);
413
414 return res > INT_MAX ? INT_MAX : res;
415}
416
417int ring__consume(struct ring *r)
418{
419 return ring__consume_n(r, INT_MAX);
420}
421
422static void user_ringbuf_unmap_ring(struct user_ring_buffer *rb)
423{
424 if (rb->consumer_pos) {
425 munmap(rb->consumer_pos, rb->page_size);
426 rb->consumer_pos = NULL;
427 }
428 if (rb->producer_pos) {
429 munmap(rb->producer_pos, rb->page_size + 2 * (rb->mask + 1));
430 rb->producer_pos = NULL;
431 }
432}
433
434void user_ring_buffer__free(struct user_ring_buffer *rb)
435{
436 if (!rb)
437 return;
438
439 user_ringbuf_unmap_ring(rb);
440
441 if (rb->epoll_fd >= 0)
442 close(rb->epoll_fd);
443
444 free(rb);
445}
446
447static int user_ringbuf_map(struct user_ring_buffer *rb, int map_fd)
448{
449 struct bpf_map_info info;
450 __u32 len = sizeof(info);
451 __u64 mmap_sz;
452 void *tmp;
453 struct epoll_event *rb_epoll;
454 int err;
455
456 memset(&info, 0, sizeof(info));
457
458 err = bpf_map_get_info_by_fd(map_fd, &info, &len);
459 if (err) {
460 err = -errno;
461 pr_warn("user ringbuf: failed to get map info for fd=%d: %s\n",
462 map_fd, errstr(err));
463 return err;
464 }
465
466 if (info.type != BPF_MAP_TYPE_USER_RINGBUF) {
467 pr_warn("user ringbuf: map fd=%d is not BPF_MAP_TYPE_USER_RINGBUF\n", map_fd);
468 return -EINVAL;
469 }
470
471 rb->map_fd = map_fd;
472 rb->mask = info.max_entries - 1;
473
474 /* Map read-only consumer page */
475 tmp = mmap(NULL, rb->page_size, PROT_READ, MAP_SHARED, map_fd, 0);
476 if (tmp == MAP_FAILED) {
477 err = -errno;
478 pr_warn("user ringbuf: failed to mmap consumer page for map fd=%d: %s\n",
479 map_fd, errstr(err));
480 return err;
481 }
482 rb->consumer_pos = tmp;
483
484 /* Map read-write the producer page and data pages. We map the data
485 * region as twice the total size of the ring buffer to allow the
486 * simple reading and writing of samples that wrap around the end of
487 * the buffer. See the kernel implementation for details.
488 */
489 mmap_sz = rb->page_size + 2 * (__u64)info.max_entries;
490 if (mmap_sz != (__u64)(size_t)mmap_sz) {
491 pr_warn("user ringbuf: ring buf size (%u) is too big\n", info.max_entries);
492 return -E2BIG;
493 }
494 tmp = mmap(NULL, (size_t)mmap_sz, PROT_READ | PROT_WRITE, MAP_SHARED,
495 map_fd, rb->page_size);
496 if (tmp == MAP_FAILED) {
497 err = -errno;
498 pr_warn("user ringbuf: failed to mmap data pages for map fd=%d: %s\n",
499 map_fd, errstr(err));
500 return err;
501 }
502
503 rb->producer_pos = tmp;
504 rb->data = tmp + rb->page_size;
505
506 rb_epoll = &rb->event;
507 rb_epoll->events = EPOLLOUT;
508 if (epoll_ctl(rb->epoll_fd, EPOLL_CTL_ADD, map_fd, rb_epoll) < 0) {
509 err = -errno;
510 pr_warn("user ringbuf: failed to epoll add map fd=%d: %s\n", map_fd, errstr(err));
511 return err;
512 }
513
514 return 0;
515}
516
517struct user_ring_buffer *
518user_ring_buffer__new(int map_fd, const struct user_ring_buffer_opts *opts)
519{
520 struct user_ring_buffer *rb;
521 int err;
522
523 if (!OPTS_VALID(opts, user_ring_buffer_opts))
524 return errno = EINVAL, NULL;
525
526 rb = calloc(1, sizeof(*rb));
527 if (!rb)
528 return errno = ENOMEM, NULL;
529
530 rb->page_size = getpagesize();
531
532 rb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
533 if (rb->epoll_fd < 0) {
534 err = -errno;
535 pr_warn("user ringbuf: failed to create epoll instance: %s\n", errstr(err));
536 goto err_out;
537 }
538
539 err = user_ringbuf_map(rb, map_fd);
540 if (err)
541 goto err_out;
542
543 return rb;
544
545err_out:
546 user_ring_buffer__free(rb);
547 return errno = -err, NULL;
548}
549
550static void user_ringbuf_commit(struct user_ring_buffer *rb, void *sample, bool discard)
551{
552 __u32 new_len;
553 struct ringbuf_hdr *hdr;
554 uintptr_t hdr_offset;
555
556 hdr_offset = rb->mask + 1 + (sample - rb->data) - BPF_RINGBUF_HDR_SZ;
557 hdr = rb->data + (hdr_offset & rb->mask);
558
559 new_len = hdr->len & ~BPF_RINGBUF_BUSY_BIT;
560 if (discard)
561 new_len |= BPF_RINGBUF_DISCARD_BIT;
562
563 /* Synchronizes with smp_load_acquire() in __bpf_user_ringbuf_peek() in
564 * the kernel.
565 */
566 __atomic_exchange_n(&hdr->len, new_len, __ATOMIC_ACQ_REL);
567}
568
569void user_ring_buffer__discard(struct user_ring_buffer *rb, void *sample)
570{
571 user_ringbuf_commit(rb, sample, true);
572}
573
574void user_ring_buffer__submit(struct user_ring_buffer *rb, void *sample)
575{
576 user_ringbuf_commit(rb, sample, false);
577}
578
579void *user_ring_buffer__reserve(struct user_ring_buffer *rb, __u32 size)
580{
581 __u32 avail_size, total_size, max_size;
582 /* 64-bit to avoid overflow in case of extreme application behavior */
583 __u64 cons_pos, prod_pos;
584 struct ringbuf_hdr *hdr;
585
586 /* The top two bits are used as special flags */
587 if (size & (BPF_RINGBUF_BUSY_BIT | BPF_RINGBUF_DISCARD_BIT))
588 return errno = E2BIG, NULL;
589
590 /* Synchronizes with smp_store_release() in __bpf_user_ringbuf_peek() in
591 * the kernel.
592 */
593 cons_pos = smp_load_acquire(rb->consumer_pos);
594 /* Synchronizes with smp_store_release() in user_ringbuf_commit() */
595 prod_pos = smp_load_acquire(rb->producer_pos);
596
597 max_size = rb->mask + 1;
598 avail_size = max_size - (prod_pos - cons_pos);
599 /* Round up total size to a multiple of 8. */
600 total_size = (size + BPF_RINGBUF_HDR_SZ + 7) / 8 * 8;
601
602 if (total_size > max_size)
603 return errno = E2BIG, NULL;
604
605 if (avail_size < total_size)
606 return errno = ENOSPC, NULL;
607
608 hdr = rb->data + (prod_pos & rb->mask);
609 hdr->len = size | BPF_RINGBUF_BUSY_BIT;
610 hdr->pad = 0;
611
612 /* Synchronizes with smp_load_acquire() in __bpf_user_ringbuf_peek() in
613 * the kernel.
614 */
615 smp_store_release(rb->producer_pos, prod_pos + total_size);
616
617 return (void *)rb->data + ((prod_pos + BPF_RINGBUF_HDR_SZ) & rb->mask);
618}
619
620static __u64 ns_elapsed_timespec(const struct timespec *start, const struct timespec *end)
621{
622 __u64 start_ns, end_ns, ns_per_s = 1000000000;
623
624 start_ns = (__u64)start->tv_sec * ns_per_s + start->tv_nsec;
625 end_ns = (__u64)end->tv_sec * ns_per_s + end->tv_nsec;
626
627 return end_ns - start_ns;
628}
629
630void *user_ring_buffer__reserve_blocking(struct user_ring_buffer *rb, __u32 size, int timeout_ms)
631{
632 void *sample;
633 int err, ms_remaining = timeout_ms;
634 struct timespec start;
635
636 if (timeout_ms < 0 && timeout_ms != -1)
637 return errno = EINVAL, NULL;
638
639 if (timeout_ms != -1) {
640 err = clock_gettime(CLOCK_MONOTONIC, &start);
641 if (err)
642 return NULL;
643 }
644
645 do {
646 int cnt, ms_elapsed;
647 struct timespec curr;
648 __u64 ns_per_ms = 1000000;
649
650 sample = user_ring_buffer__reserve(rb, size);
651 if (sample)
652 return sample;
653 else if (errno != ENOSPC)
654 return NULL;
655
656 /* The kernel guarantees at least one event notification
657 * delivery whenever at least one sample is drained from the
658 * ring buffer in an invocation to bpf_ringbuf_drain(). Other
659 * additional events may be delivered at any time, but only one
660 * event is guaranteed per bpf_ringbuf_drain() invocation,
661 * provided that a sample is drained, and the BPF program did
662 * not pass BPF_RB_NO_WAKEUP to bpf_ringbuf_drain(). If
663 * BPF_RB_FORCE_WAKEUP is passed to bpf_ringbuf_drain(), a
664 * wakeup event will be delivered even if no samples are
665 * drained.
666 */
667 cnt = epoll_wait(rb->epoll_fd, &rb->event, 1, ms_remaining);
668 if (cnt < 0)
669 return NULL;
670
671 if (timeout_ms == -1)
672 continue;
673
674 err = clock_gettime(CLOCK_MONOTONIC, &curr);
675 if (err)
676 return NULL;
677
678 ms_elapsed = ns_elapsed_timespec(&start, &curr) / ns_per_ms;
679 ms_remaining = timeout_ms - ms_elapsed;
680 } while (ms_remaining > 0);
681
682 /* Try one more time to reserve a sample after the specified timeout has elapsed. */
683 return user_ring_buffer__reserve(rb, size);
684}